In the recent growing trends among electronic devices towards the use of the higher frequency, the capacitors nowadays are required to be superior in the impedance characteristic at the higher frequency region. In order to meeting such requirements, solid electrolytic capacitors have been developed using a conductive polymer having high electrical conductivity as a solid electrolyte.
There are also strong requests that those solid electrolytic capacitors for use in the periphery of microprocessors (CPU) in personal computers, etc. are compact in size yet having a large capacitance. As the results of the shift towards the higher frequency region, reduction of the equivalent series inductance (ESL) is urged, besides reduction of the equivalent series resistance (ESR). The capacitors are further required to provide superior performance in the noise reduction and in the transient response capability. Various efforts are made in order to satisfy these demands.
The solid electrolytic capacitors are used specifically in the following sectors such as the power supply circuits, digital circuits and the like circuits where the low impedance at high frequency region is specially required. For the purpose of precise inspection of these electrolytic capacitors with respect to the impedance, the following inspection device has been proposed.
FIG. 13 is a conceptual view of a conventional inspection device used for measuring the impedance of solid electrolytic capacitors. In the drawing, the portion surrounded with dotted lines represents impedance measurer 50 illustrated simplified. Impedance measurer 50 includes alternating power supply 51, current limiting resistor 52, current detector 53 for detecting a current flow to capacitor 54, voltage detector 55, current terminals 56, 57 and voltage terminals 58, 59.
Current probes 60, 61 and voltage probes 62, 63 are used for making contact with electrodes of capacitor 54 which is an object of measurement, when measuring the impedance. Resistor 65 is provided between lead end 64 drawn from current terminal 56 and current probe 60 via, while resistor 67 is provided between lead end 66 drawn from voltage terminal 58 and voltage probe 62. Detection resistor 68 is provided between lead end 64 and lead end 66. Likewise, there are resistor 70 between current probe 61 and lead end 69, resistor 72 between voltage probe 63 and lead end 71, and detection resistor 73 between lead end 69 and lead end 71. It is preferred that detection resistors 68, 73 have sufficiently greater resistance value (10Ω-100Ω) than the contact resistance of probes 60-63; however, detection resistors 78, 73 can be eliminated.
FIG. 14 is an equivalent circuit diagram of the impedance inspection device shown in FIG. 13; the portion surrounded with dotted lines represents impedance measurer 50 illustrated simplified. Capacitor 54 has capacitance 54A and equivalent series resistance 54B. There are resistivity 65A and inductive component 74 between current probe 60 and lead end 64 via resistor 65. Likewise, there are resistivity 70A and inductive component 75 between current probe 61 and lead end 69 via resistor 70. There are resistivity 67A and inductive component 76 between voltage probe 62 and lead end 66 via resistor 67. There are resistivity 72A and inductive component 77 between voltage probe 63 and lead end 71 via resistor 72.
In the above-described setup, the impedance of capacitor 54 is measured as follows: At first, it is corrected at open state and at short-circuit state without setting capacitor 54. And then, current probes 60, 61 and voltage probes 62, 63 are brought to make contact with the electrodes of capacitor 54 at both ends, for having an alternating current from alternating power supply 51 applied between current probes 60 and 61. Voltage caused at the both ends of capacitor 54 is detected by voltage detector 55 through voltage probes 62, 63. Current (I) and voltage (V) are detected at this moment by voltage detector 55 and current detector 53, and impedance Z is calculated using the Formula Z=V/I.
Current probes 60, 61 and voltage probes 62, 63 are in contact with the electrodes of capacitor 54. Therefore, resistivity 65A, 70A, 67A, 72A as well as inductive component 74, 75, 76, 77 of probes 60-63 are corrected to be 0 on the electrical equivalent circuit. In this way, impedance measurer 50 can measure the impedance precisely. Such an impedance inspection device is disclosed in Japanese Patent Unexamined Publication No. 2001-35759, for example.
The above-described conventional inspection device aims to measure the impedance of capacitor 54 which is an object of measurement, on a production line within a very short time. So, the ESL of a capacitor can be known based on the measurement results. The accuracy level of the measurement, however, is not high enough for measuring the impedance of solid electrolytic capacitors whose ESL is expected to be low.